1. Field of the Invention
This invention relates to high-speed analog multipliers. More particularly, this invention relates to a novel analog multiplier which employs a minimum number of high-speed logic devices for producing multiplied analog voltage results or alternatively distortion free absolute voltage values of analog inputs.
2. Description of the Prior Art
Analog multipliers are known to be relatively slow devices and heretofore have been limited to a speed of around 25 megahertz before distortion renders the output unusable.
Absolute value detectors, such as full wave bridge rectifiers, have been limited to the same range of frequencies of around 25 megahertz at the output and even then distortion is present and so that such circuits are not useful where extreme accuracy is is desired.
Absolute value detectors have been produced employing full wave rectification of an A.C. signal produced across the secondary coil of a transformer from an input signal applied to the primary coil of the transformer. While such rectifiers save at least two diodes over a full wave bridge rectifier, such devices are slower and have an output which is distorted not only by the diodes but by the inductive reactance of the transformer.
High-speed full wave rectifiers which employ diodes are limited to the operable frequency of the diodes and further are limited to the distortion characteristics or efficiency of the type of diode being employed. Presently, commercially available diodes are subject to distortion which limits their use to a level below their maximum operable frequency. It is well known that there is an accompanying DC offset when employing diodes in full wave rectifiers. Further, since diode rectifiers employ a plurality of diodes, operation of unmatched diodes at high-speed causes amplitude distortion due to imperfect balance of diodes. It is possible to manufacture diodes which can be operated at higher speeds than those which are generally commercially available. However, the distortion and DC offset will always be present when using diodes and a full wave rectifier.
It would be extremely desirable to provide a high-speed analog multiplier which is also operable as an absolute value detector or a high-speed chopper for producing distortion free output signals.